Physician Investigator (Cl) Anesthesia, Critical Care and Pain Medicine, Mass General Research Institute

Professor of Anaesthesia Harvard Medical School

Anesthetist Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital

M.D.; Ph.D. Harvard Medical School 1989

allosteric drug mechanisms; alphaxalone; anesthetic drug development; anesthetics; anesthetics general; anesthetics inhalation; anesthetics intravenous; etomidate; general anesthesia; glycine; ion channel function; ion channel gating; ligand-gated ion channels; propofol; receptors gaba-a; receptors nicotinic

My broad research aims are to understand where and how sedative/hypnotics act at the molecular level, in order to guide development of improved drugs to help patients when they are most vulnerable: under general anesthesia.  The molecular targets we study are anesthetic sensitive pentameric ligand-gated ion channels, including gamma-aminobutyric acid-A (GABA_A), glycine, nicotinic acetylcholine (nACh), and serotonin-3 (5HT3) receptors.  These channels modulate inter-neuronal communication in the central nervous system.  The drugs of greatest interest are potent intravenous agents including etomidate, propofol, alphaxalone, and barbiturates.  Most of these drugs produce their major anesthetic effects by enhancing the activity of specific GABA_A receptors.

To study drug effects on these ion channels, we express cloned receptor subunit DNAs in cells and use voltage-clamp electrophysiological methods in either whole cells or in excised membrane patches.  We developed a unique flexible “artificial synapse” device that enables sub-millisecond switching between up to four different superfusate solutions for patch-clamp experiments.  This technique has enabled us to study channel kinetics, including silent state transitions, in great detail. 

Through quantitative pharmacological-mechanistic analysis, we established that equilibrium allosteric models could elegantly account for the actions of etomidate on GABA_A receptors, and have demonstrated that other anesthetics act by similar mechanisms, but via different sets of sites.  We have also applied allosteric principles to kinetic models that replicate activation, desensitization and deactivation of GABA_A and 5HT3A receptors.

Allosteric models provide a framework for design and analysis of our structure-function studies, in mutated ion channels.  Pharmacological data from mutant channels can be analyzed to infer whether mutations alter anesthetic binding interactions, drug efficacy, and/or channel gating.  This approach has been used to map anesthetic binding pockets formed between transmembrane elements from two adjacent subunits of GABA_A receptors. 

Complementing our molecular studies are translational studies using zebrafish for both drug screening and mechanistic studies.  Zebrafish are an efficient model for screening drug libraries to identify novel sedative-hypnotics that may have clinical value.   Zebrafish also facilitate studies of sedative drug interactions that may have clinical correlates.  Additionally, we are creating transgenic zebrafish to study the role of specific receptor subunits in anesthetic sensitivity.

Another collaborative project, with my colleague Dr. Douglas Raines (MGH DACCPM), aims to develop improved clinical anesthetics based on etomidate.  We help design new anesthetic drugs, test their activity in ion channel targets, and also test their potential toxicities.